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Method For Decoding Code 39 or Interleaved 2 of 5 Labels

IP.com Disclosure Number: IPCOM000048643D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Laurer, GJ: AUTHOR

Abstract

This article describes a technique for decoding "code 39" or "inter leaved 2 of 5" bar-coded labels which minimizes the effects of ink spread to increase label tolerances and decode reliability. Very generally, each combination of a bar (black) and a space (white) is compared to the following, overlapping combination of a space and a bar. A series of ratios are derived which can be used to decode the character.

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Method For Decoding Code 39 or Interleaved 2 of 5 Labels

This article describes a technique for decoding "code 39" or "inter leaved 2 of 5" bar-coded labels which minimizes the effects of ink spread to increase label tolerances and decode reliability. Very generally, each combination of a bar (black) and a space (white) is compared to the following, overlapping combination of a space and a bar. A series of ratios are derived which can be used to decode the character.

Referring to Fig. 1, a "code 39" character consists of five black bars B1 through B5 interleaved with four white bars W1 through W4. There are only two bar widths, wide and narrow. Two of the five black bars are wide, while three are narrow. One of the four white bars is wide, while four are narrow. By varying the positions of the wide bars and spaces within the character, forty characters can be defined. Four special characters can also be obtained by violating the stated rules.

A "code 39" character can be decoded by comparing the widths of the black bars B1 through B5 to each other to determine which are wide and which are narrow. Similarly, the widths of the white bars W1 through W4 are compared to each other to determine which white bars are wide and which are narrow. When the wide bars have been identified, a table look-up can be performed to decode the character.

The above-described decoding technique is reasonably tolerant of systematic errors (e.g., uniform ink spread or ink shrink), but is less tolerant of random errors. A decoding method which is more tolerant of random errors and which is highly tolerant of systematic errors is described with reference to Fig. 2. According to this decoding method, the character is divided into eight, overlapping black/white bar pairs. Seven successive ratios are formed for each character by comparing the width of each pair to the width of the succeeding, overlapping pair. For example, ratio R1 equals A1/A2, ratio R2 equals A2/A3, ... ratio R7 equals A7/A8. Once the seven ratios have been calculated, a ta...